When they had escaped Miranda and Garth wanted to go back to steal another crystal. Omega teleported them down to planet Zeron, right into the crystal chamber. There, it all went wrong.
As the alarm went off, Varon bumps the gun out of Garth's hand because Garth had intentions to shoot at him. Miranda takes the lazergun and shot Garth down. When Varon turns around Miranda gives him an injection to sleep. Varon doesn't sleep immediately and bumps the lazergun out of her hands and he shoots Miranda down.
Omega teleports Varon back to the spaceship, which they split under the two of them.